Two years ago I purchased a syska power bank which is 11000 mah power pack. This is available offline as well as online. I found it really so helpful, it can charge upto 3 to 4 time completely my phone.
The mobile charging time through the power bank is same as we use the normal charge. It take upto 3 hours to charge the power bank completely. Don’t have any problems with working. And the best thing it has been two and half year of using this syska 11000 mah power bank and not facing any issue.
An average weight to carry in the pocket, around double the weight of mobile phone. It is available in various colors but because of regular use I bought in black color, which doesn’t look dirty after using for a long time.
I changed the USB cable because by default a very short cable they sent. Well this is with every power bank, you can use your own if you want a sufficient length cable. But I suggest you please keep a short one also for the somewhat fast charging. Short length cable take little bit less time to charge the mobile.